1. Field of the Invention
The present invention relates generally to computer-assisted drafting (CAD) systems, and in particular, to a method, apparatus, and article of manufacture for tolerant, persistent naming of loft features in a parametric feature-based, solid modeling system.
2. Description of the Related Art
Over the last decade, designers have changed their fundamental approach to CAD systems, moving from 2D drawing systems to 3D solid modeling systems. New software makes solid modeling technology available and affordable to virtually anyone.
Solid modeling is a technique that allows designers to create dimensionally accurate 3D solid models in 3D space represented within a computer, rather than traditional 2D drawings. 3D solid models include significantly more engineering data than 2D drawings, including the volume, bounding surfaces, and edges of a design.
With the graphics capabilities of today""s computers, these 3D solid models may be viewed and manipulated on a monitor. In addition to providing better visualization, 3D solid models may be used to automatically produce 2D drawing views, and can be shared with manufacturing applications and the like.
Some 3D solid modeling systems generate parametric feature-based models. A parametric feature-based model is comprised of intelligent features, such as holes, fillets, and chamfers. The geometry of the parametric feature-based model is defined by underlying mathematical relationships (i.e., parameters) rather than by simple unrelated dimensions, which makes them easier to modify. These systems preserve design intent and try to maintain it after every change to the model.
Moreover, these features are automatically adjusted as the model is modified. The system computes any related changes to parts of the model that are dependent on a parameter, and automatically updates the entire model when the parameter is changed. For example, a through-hole will always go completely through a specified part, even if the part""s dimensions are changed.
Lofting is a useful technique for generating complex shapes in feature-based parametric solid modeling systems. Typically, the user provides the system with input in the form of a number of 2D cross-sections, in a specific order, along with parameters such as tangency conditions, take-off angles, and weight factors. The system then processes this input into a loft feature of the 3D solid model.
The use of a loft feature within a parametric modeling system requires the capabilities of persistently naming topology produced by the loft feature. These names normally exist on the topological entities (faces, edges, vertices) of the loft feature. One of the desirable traits of such names is that they be invariant (or tolerant) to changes made in the defining geometry of the loft.
Most prior art systems do not generate and maintain unique persistent names that are tolerant to change in the defining data of a loft feature. In such prior art systems, downstream features referencing the loft feature will fail to update during editing operations involving partial or drastic topology changes.
Consider, for example, the following publications:
Kripac, J., xe2x80x9cA mechanism for persistently naming topological entities in history-based parametric solid modelsxe2x80x9d, Computer-Aided Design, Vol. 29(2): pp. 113-122, 1997;
Hoffman, C. M., Capoyleas, V., Chen, X., xe2x80x9cGeneric Naming in Generative, Constraint-Based Designxe2x80x9d, Computer-Aided Design, Vol. 28, pp. 17-26, 1996;
all of which are incorporated by reference herein.
The prior art systems described in the above publications expend no effort to look at the previous state of the loft feature during editing operations to preserve the names on the topological entities of the updated feature. The previous state of the loft feature contains important information, which the current invention uses to achieve unique and persistent names that are tolerant to partial topology changes.
Tolerant naming would allow other designs features (e.g., downstream features) in the model to establish and resolve dependencies to the loft feature, notwithstanding topological changes to the loft feature, such as adding/deleting other feature, changing the order of cross-sections in the loft feature, adding/deleting one or more cross-sections in the loft feature, etc. Thus, there is a need in the art for unique persistent naming of loft feature that are tolerant in a parametric feature-based solid modeling system.
To address the requirements described above, the present invention discloses a computer-implemented, parametric feature-based, solid modeling system that generates tolerant and unique persistent names for the topological entities of a loft feature. The system preserves and updates the names using a similarity analysis, so that they are tolerant to partial topology changes in the loft feature and any model containing the loft feature.